The present invention relates to multi-layer products, and an apparatus and method for the injection molding of same. More specifically, it relates to a back-flow control valve for an injection molding apparatus.
Multi-cavity injection molding apparatus for making multi-layer molded products, such as protective containers for food, preforms for beverage bottles, and closures, are well-known. One or more layers of one material are typically molded within, or together with, one or more layers of another material, to form the molded product. At least one of these layers is usually a barrier layer formed from a barrier material to protect the contents of the molded product. Since the barrier material is expensive, typically only a very thin barrier layer is used in the molded product. It is also generally desirable to have this thin barrier layer uniformly and evenly distributed (i.e., well-balanced) throughout the molded product to provide the proper protection for the contents of the molded product.
One common method for injection molding of products is sequential injection molding. In sequential injection molding, one or more materials are injected into a cavity in a specified order or sequence. For instance, a preform or closure material may be injected into a cavity first, followed by the injection of a barrier material into the cavity second. Sequential injection molding may be used alone to form molded products, or may be combined with coinjection or simultaneous injection molding.
Problems can occur in sequential injection molding, however, when one material back-flows into the melt passage of another material. Such mixing of the two materials outside of the cavity can cause problems with the flow of materials through the injection molding apparatus, and often results in an undesirable or low quality molded product. For example, if a preform or closure material that is being injected into a cavity back-flows into a melt passage carrying a barrier material, it may be difficult for the barrier material to flow through the injection molding apparatus during its injection cycle into the cavity. Moreover, the resulting molded products may not have the proper or intended composition of materials, since the injection of the barrier material into the cavity will also include the preform or closure material that has back-flowed into the melt passage of the barrier material.
Accordingly, it would be desirable to have an apparatus and method for injection molding that overcomes the problems associated with the prior art by having a control for the back-flow of one material into the melt passage of another material. An apparatus and method for injection molding that restricts or substantially prevents the back-flow of one material into the melt passage of another material would not only produce a more efficient injection molding apparatus and method, but would also result in a higher quality molded product.
The present invention provides an injection molding apparatus comprising a first melt passage for the flow of a first material, and a second melt passage in communication with the first melt passage for the flow of a second material. The injection molding apparatus of the present invention also comprises a valve pin that passes through the second melt passage. The valve pin has a first portion allowing the flow of the second material through the second melt passage, and a second portion restricting the flow of the first material and the second material through the second melt passage.
In addition, the present invention provides a back-flow control valve in combination with a melt passage of an injection molding apparatus. The back-flow control valve comprises a first portion for permitting flow of material through the melt passage, and a second portion for restricting flow of material through the melt passage.
The present invention also provides an injection molding apparatus comprising a manifold having at least a portion of a melt passage, and a nozzle having a melt channel in communication with the melt passage. The injection molding apparatus further comprises a cavity aligned with the melt channel of the nozzle. Also, the injection molding apparatus comprises a valve member having a first portion for restricting flow of material through the melt passage, and a second portion for restricting flow of material from the melt channel into the cavity.
Moreover, the present invention also provides a method for injection molding comprising the step of injecting a material into a melt passage having a first section and a second section. The method of the present invention further comprises the step of positioning a first portion of a valve pin between the first and second sections to permit flow of the material through the melt passage. The method of the present invention also comprises the step of positioning a second portion of the valve pin between the first and second sections to restrict flow of the material through the melt passage.